Apple Watch Series 5 has a water resistance rating of 50 meters under ISO standard 22810:2010. This means that they may be used for shallow-water activities like swimming in a pool or ocean. However, they should not be used for scuba diving, waterskiing, or other activities involving high-velocity water or submersion below shallow depth.
Apple Watch Series 5 (GPS + Cellular) can use a cellular connection for Emergency SOS. To use Emergency SOS on an Apple Watch without cellular, your iPhone needs to be nearby. If your iPhone isn’t nearby, your Apple Watch needs to be connected to a known Wi-Fi network and you must set up Wi-Fi Calling.